The present invention relates to a method of producing trimethylolalkane by a reaction between n-alkanal and formaldehyde in the presence of tertiary amine and water.
Trimethylolalkane is useful as a raw material for an alkyd resin, a polyurethane resin, a (un)saturated polyester resin, a synthetic lubricating oil, a surfactant, a reactive monomer and the like.
As a known method of producing trimethylolalkane, n-alkanal is reacted with formaldehyde in the presence of a hydroxide of an alkaline metal or an alkali earth metal. In this method, alkaline metal formate or alkali earth metal formate is produced as a by-product. Trimethylolalkane is catalytically thermally decomposed by the formate. Accordingly, in conducting distillation, a general isolating and purifying technique for trimethylolalkane, it is necessary to sufficiently separate trimethylolalkane from the alkaline metal formate or the alkali earth metal formate in order to prevent the yield of trimethylolalkane from being lowered by the catalytic thermal decomposition. Thus, the separation is troublesome.
As an improvement of the aforementioned method, a method of producing trimethylolalkane by using tertiary amine and water instead of the hydroxide of an alkaline metal or an alkali earth metal has been proposed (West Germany Patent No. 1952738). In this method using tertiary amine the formate produced as a by-product is a salt of tertiary amine with formic acid, which does not catalytically thermally decompose trimethylolalkane. Therefore, the thermal decomposition of trimethylolalkane can be suppressed. In this method, the salt of tertiary amine with formic acid is separated from trimethylolalkane by utilizing a difference in the boiling points between the salt and trimethylolalkane.
However, the aforementioned improved method has the following disadvantage. In the separation of a salt of tertiary amine with formic acid from trimethylolalkane by using the difference in the boiling points therebetween, formic acid produced by thermal dissociation of the salt reacts with trimethylolalkane to produce a formate of trimethylolalkane. As a result, the yield of trimethylolalkane is lowered.